The invention relates to vehicles, and more particularly to vehicles including a power transmission mechanism comprising variable-ratio gearing driven by way of a hydrodynamic torque converter having a hydraulically-engaged lock-up clutch, and also including hydraulically-engaged friction means comprising either clutch and/or brake means for establishing a ratio in the gearing or brake means for bringing the vehicle to rest, or both such means.
The object of the invention is to modulate operation of the friction means by retarding the engagement thereof so that ratio variations in the gearing occur, and/or the vehicle is brought to rest, more smoothly.